In the commercial production of rubber modified resins of the type wherein rubber particles of alkadiene rubber grafted with a styrene-type monomer and acrylonitrile-type monomer are generally uniformly dispersed in a matrix of a copolymer of styrene-type monomer and acrylonitrile-type monomer, which resins are sometimes termed ABS resins, it has heretofore been a common commercial practice to use either suspension or emulsion polymerization procedures for the preparation thereof. A given product resin is produced either as a result of a single batch polymerization or as a result of several batch polymerizations followed by a physical blending procedure involving mixing of preformed graft copolymers with other graft copolymers or with ungrafted copolymer. Because of the inherent cost, complexity and sensitivity associated with such manufacturing technology, the art has recently been attempting to develop different techniques which would permit one to manufacture such resins using cheaper, less complex, highly reliable procedures and equipment. A particularly promising different technique would involve the use of mass polymerization which avoids such problems as product separation and recovery from the water used for suspension or emulsion polymerization.
To prepare ABS resins by all-mass polymerization technology has been heretofore proposed, but the practical realization of such a manufacturing route on a commercial scale is full of problems because of the difficulties of producing a product resin which is cheap enough to be competitive and still has the necessary and desirable physical properties for molding and extruding and for formed, manufactured product applications. Because of these difficulties, the art would like to blend some of the mass polymerization technology with some of the emulsion and/or suspension technology in an overall process. So far as is presently known, however, the previously proposed hybrid routes involving such a mixture of polymerization technologies to make ABS type resins have generally not been commercialized for a variety of cost and product quality related reasons.
There has now been invented a new and very useful process for making ABS and other related resins which utilizes both mass or bulk polymerization and emulsion polymerization technologies. This new process involves grafting an alkadiene elastomer with a mixture of styrene-type and acrylonitrile-type monomers by emulsion polymerization techniques to produce a grafted rubber latex, mixing with such latex a mixture of at least one of the same monoethylenically unsaturated monomers and at least one saturated styrene-acrylonitrile copolymer solvent in an amount of at least 5 percent by weight of such saturated solvent based on the total weight of monomers and solvent, coagulating said grafted rubber particles, separating water from said mixture and subjecting the resulting dispersion of grafted rubber in said solvent and monomer mixture to mass or bulk polymerization.
The process of the present invention offers many advantages over the prior art. The monomer-solvent mixture serves to transfer the grafted rubber polymer into the organic solvent phase without substantially altering the size of the graft rubber particles and renders the water present in the latex emulsion largely separable from the dispersion of graft rubber particles in the monomer-solvent mixture. The mixed saturated solvent can be readily separated from the product of mass or bulk polymerization by devolatilization along with the unreacted alkenenitrile and monovinylidene aromatic monomers. Likewise such solvent can be recycled along with said recovered monomers to serve as additional dewatering solvent for fresh graft rubber latex in a continuous process.